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| Titel |
Dynamics of nitrogen oxides and ozone above and within a mixed hardwood forest in northern Michigan |
| VerfasserIn |
B. Seok, D. Helmig, L. Ganzeveld, M. W. Williams, C. S. Vogel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 15 ; Nr. 13, no. 15 (2013-08-01), S.7301-7320 |
| Datensatznummer |
250018793
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| Publikation (Nr.) |
 copernicus.org/acp-13-7301-2013.pdf |
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| Zusammenfassung |
| The dynamic behavior of nitrogen oxides (NOx = NO + NO2) and ozone
(O3) above and within the canopy at the University of Michigan
Biological Station AmeriFlux (UMBS Flux) site was investigated by continuous
multi-height vertical gradient measurements during the summer and the fall of
2008. A daily maximum in nitric oxide (NO) mixing ratios was
consistently observed during the morning hours between 06:00 and 09:00 EST
above the canopy. Daily NO maxima ranged between 0.1 and 2 ppbv (with
a median of 0.3 ppbv), which were 2 to 20 times above the atmospheric
background. The sources and causes of the morning NO maximum were
evaluated using NOx and O3 measurements and synoptic and
micrometeorological data. Numerical simulations with a multi-layer
canopy-exchange model were done to further support this analysis. The
observations indicated that the morning NO maximum was caused by the
photolysis of NO2 from non-local air masses, which were transported
into the canopy from aloft during the morning breakup of the nocturnal
boundary layer. The analysis of simulated process tendencies indicated that
the downward turbulent transport of NOx into the canopy compensates
for the removal of NOx through chemistry and dry deposition. The
sensitivity of NOx and O3 concentrations to soil and foliage
NOx emissions was also assessed with the model. Uncertainties
associated with the emissions of NOx from the soil or from
leaf-surface nitrate photolysis did not explain the observed diurnal behavior
in NOx (and O3) and, in particular, the morning peak in
NOx mixing ratios. However, a ~30% increase in early
morning NOx and NO peak mixing ratios was simulated when a
foliage exchange NO2 compensation point was considered. This increase
suggests the potential importance of leaf-level, bidirectional exchange of
NO2 in understanding the observed temporal variability in NOx
at UMBS. |
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